High density plasma CVD process for gapfill into high aspect ratio features

ABSTRACT

A method of depositing a film on a substrate disposed in a substrate processing chamber. In one embodiment the method includes depositing a first portion of the film to at partially fill a gap formed between to adjacent features formed on the substrate. The first portion of film is deposited using a high density plasma formed from a first gaseous mixture flown into the process chamber. The film deposition process is then stopped before or shortly after the entry of the gap pinches off and the film is etched to widen entry to the gap using a two step etching process that includes a first physical etch step and a subsequent chemical etch step. The physical etch step sputter etches the first portion of film by forming a plasma from a sputtering agent introduced into the processing chamber and biasing the plasma towards the substrate. After the physical etching step, the film is chemically etched by forming a plasma from a reactive etchant gas introduced into the processing chamber. After the etching sequence is complete and entry to the gap has been widened, a second portion of the film is deposited over the first portion to further fill the gap by forming a high density plasma from a second gaseous mixture flown into the process chamber.

BACKGROUND OF THE INVENTION

[0001] One of the primary steps in the fabrication of modernsemiconductor devices is the formation of a thin film on a semiconductorsubstrate by chemical reaction of gases. Such a deposition process isreferred to as chemical vapor deposition (“CVD”). Conventional thermalCVD processes supply reactive gases to the substrate surface whereheat-induced chemical reactions take place to produce a desired film.Plasma-enhanced CVD (“PECVD”) techniques, on the other hand, promoteexcitation and/or dissociation of the reactant gases by the applicationof radio-frequency (“RF”) energy to a reaction zone near the substratesurface, thereby creating a plasma. The high reactivity of the speciesin the plasma reduces the energy required for a chemical reaction totake place, and thus lowers the temperature required for such CVDprocesses as compared to conventional thermal CVD processes. Theseadvantages are further exploited by high-density-plasma (“HDP”) CVDtechniques, in which a dense plasma is formed at low vacuum pressures sothat the plasma species are even more reactive.

[0002] Any of these CVD techniques may used to deposit conductive orinsulative films during the fabrication of integrated circuits. Forapplications such as the deposition of insulation films as premetal orintermetal dielectric layers in an integrated circuit or for shallowtrench isolation, one important physical property of the CVD film is itsability to completely fill gaps between adjacent structures withoutleaving voids within the gap. This property is referred to as the film'sgapfill capability. Gaps that may require filling include spaces betweenadjacent raised structures such as transistor gates, conductive lines,etched trenches or the like.

[0003] As semiconductor device geometries have decreased in size overthe years, the ratio of the height of such gaps to their width, theso-called “aspect ratio,” has dramatically increased. Gaps having acombination of a high aspect ratio and a small width present a challengefor semiconductor manufacturers to fill completely. In short, thechallenge usually is to prevent the deposited film from growing in amanner that closes off the gap before it is filled. Failure to fill thegap completely results in the formation of voids in the deposited layer,which may adversely affect device operation, for example by trappingundesirable impurities.

[0004] One process that the semiconductor industry has developed toimprove gapfill capability of insulation films uses a multistepdeposition and etching process. Such a process is often referred to as adeposition/etch/deposition (“dep/etch/dep”) process. Such dep/etch/depprocesses divide the deposition of the gapfill layer into two or moresteps separated by a plasma etch step. The plasma etch step etches theupper corners of the first deposited film more than the film portiondeposited on the sidewall and lower portion of the gap, thereby wideningthe gap and enabling the subsequent deposition step to fill the gapwithout prematurely closing it off. Typically, dep/etch/dep processescan be used to fill higher-aspect-ratio small-width gaps than a standarddeposition step for the particular chemistry would allow.

[0005] Most of the early dep/etch/dep processes known to the inventorswere limited to thermal CVD and PECVD processes. HDP-CVD processesgenerally have superior gapfill capabilities as compared to these othertypes of CVD processes because HDP-CVD deposition process provide for asputtering component to the deposition process simultaneous with filmgrowth. For this reason, HDP-CVD techniques are sometimes referred to assimultaneous dep/etch processes.

[0006] It has been found in practice, however, that while HDP-CVDprocesses generally have better gapfill capabilities than similarnon-HDP-CVD processes, for certain gap widths there remains a limit tothe aspect ratio of gaps that can be filled. In view of this limit,semiconductor manufacturers have developed various dep/etch/deptechniques for HDP-CVD processes. All of the techniques known to thepresent inventors employ a single step etch process in which thematerial deposited in the preceding deposition step is etched usingeither a physical etch (i.e., anisotropic etch), a chemical etch (i.e.,isotropic etch) or an etch step that simultaneously combines physicaland chemical components. While a number of these processes are able toproduce films having improved gapfill characteristics as compared toother CVD techniques, further improvements and/or alternative approachesare desirable. Such improved processes are particularly desirable inlight of the aggressive gapfill challenges presented by integratedcircuit designs employing minimum feature sizes of 0.10 microns andless.

BRIEF SUMMARY OF THE INVENTION

[0007] Embodiments of the present invention pertain to a high densityplasma CVD dep/etch/dep gapfill process that employs a multistep etchingtechnique to widen the entry to the gap being filled after the firstdeposition step. Embodiments of the invention have superior gapfillcapabilities as compared to similar non-dep/etch/dep HDP-CVD processes.

[0008] One embodiment of the invention provides a method of depositing adielectric film to fill a gap or trench formed between two adjacentraised features formed on the substrate. The method includes depositinga first portion of the dielectric film using a high density plasmaformed from a first gaseous mixture flown into the process chamber to atleast partially fill the gap. The film deposition process is thenstopped before or shortly after the entry of the gap pinches off and thefilm is etched to widen entry to the gap using a multistep etchingprocess that includes a first physical etch step and a subsequentchemical etch step. The physical etch step sputter etches the firstportion of film by forming a plasma from a sputtering agent introducedinto the processing chamber and biasing the plasma towards thesubstrate. After the physical etching step, the film is chemicallyetched by forming a plasma from a reactive etchant gas introduced intothe processing chamber. After the etching sequence is complete and entryto the gap has been widened, a second portion of the film is depositedover the first portion by forming a high density plasma from a secondgaseous mixture flown into the process chamber to further fill the gap.

[0009] According to another embodiment, a method of depositing a silicaglass film on a substrate having a trench formed between adjacent raisedsurfaces of the substrate is disclosed. The method comprisestransferring the substrate into a substrate processing chamber anddepositing a first portion of the silica glass film over the substrateand within the trench by forming a high density plasma process that hassimultaneous deposition and sputtering components from a firstdeposition gas comprising a silicon source and an oxygen source. Next,deposition of the silica glass film is stopped and a multistep etchingprocess is begun. The first step of the etching process sputter etchesthe first portion of the film by biasing a high density plasma formedfrom a sputtering agent introduced into the processing chamber towardsthe substrate. The next step chemically etches the first portion of thefilm with reactive species formed from an etchant gas. After themultistep etching sequence, a second portion of the silica glass film isdeposited over the substrate and within the trench by forming a highdensity plasma process that has simultaneous deposition and sputteringcomponents from a second deposition gas comprising a silicon source andan oxygen source.

[0010] These and other embodiments of the invention along with many ofits advantages and features are described in more detail in conjunctionwith the text below and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a flowchart depicting the steps associated with oneembodiment of the present invention;

[0012] FIGS. 2A-2D are simplified cross-sectional views of a substratethat illustrate the profile of film growth as the substrate is processedaccording to the steps depicted in FIG. 1;

[0013]FIG. 3A is a simplified, cross-sectional view of an exemplarysubstrate processing system with which embodiments of the presentinvention may be used;

[0014]FIG. 3B is a simplified cross-sectional view of a gas ring thatmay be used in conjunction with the exemplary CVD processing chamber ofFIG. 3A; and

[0015]FIG. 4 is a flowchart depicting the steps associated with anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Embodiments of the invention pertain to a multistep high densityplasma process for depositing dielectric material into high aspect ratiofeatures. Embodiments of the invention permit the dielectric material tobe deposited with substantially 100% gapfill at increased aspect ratiosas compared to similar non-dep/etch/dep processes. For example, for gapshaving a width of 0.13 microns substantially 100% gapfill is can beachieved by embodiments of the invention for aspect ratios of 6:1 andeven higher. Embodiments of the invention are useful for a variety ofdifferent applications and are particularly useful for the fabricationof integrated circuits having minimum feature sizes of 0.13 microns orless.

[0017] In some embodiments of the invention, the dep/etch/dep process isperformed as a continuous process without the need for separate plasmageneration in each of the individual phases. The continuity of such aprocess results in increased process uniformity across a wafer. Inparticular, such continuity results in the same gas distribution for thedeposition gases and for the etchant gas during their respective phases.Thus, even if this distribution includes some degree of nonuniformity,the multiple phases of the process tend to compensate. In regions of awafer where the deposition is greater than average, the degree ofetching tends to similarly be greater than average. Conversely, inregions of a wafer where the deposition is less than average, the degreeof etching tends to similarly be less than average.

[0018] In order to better appreciate and understand the presentinvention, reference is made to FIG. 1, which is a flowchart depictingthe steps associated with one embodiment of the invention, and FIGS.2A-2E, which are simplified cross-sectional views of a substrate thatillustrate the profile of film growth as the substrate is processedaccording to the steps depicted in FIG. 1. The process discussed belowwith respect to FIGS. 1 and 2A-2E is for an undoped silica glass (USG)film that may be used, for example, in a shallow trench isolation (STI)application. It is to be understood, however, that the techniques of thepresent invention are applicable to other applications such asintermetal dielectric (IMD) layers and premetal dielectric (PMD) amongothers. Also, the techniques of the present invention are applicable tothe deposition of a variety of materials using HDP-CVD techniques. Thesematerials, the use of which is application dependent, includephosphorous silica glass (PSG), boron-doped silicate glass (BSG),borophosphosilicate glass (BPGS), carbon-doped silica glass (SiOC) andsilicon oxynitride among others.

[0019] As shown in FIG. 1, the process starts by loading a substrateinto a substrate processing chamber (step 10). Referring to FIG. 2A, thesubstrate has one or more gaps formed between adjacent raised features.The raised features may be, for example, adjacent metal lines,transistor gates or other features. In FIGS. 2A-2E, however, the raisedfeatures represent areas of a silicon substrate 20 between trenchesetched in the substrate, such as trenches in a shallow trench isolation(STI) structure. The STI structure shown in FIGS. 2A-2E also includessilicon nitride portions 22 above the raised features and a siliconoxide interface or glue layer 24 between the silicon nitride portions 22and silicon substrate 20. Also shown in FIGS. 2A-2E is an oxide linerlayer 26, such as an in situ steam generation (ISSG) oxide or otherthermal oxide layer. In some applications trench 15 has an aspect ratioof between about 6:1 to 8:1 and the formation of a highly conformal filmsuch as oxide liner 26 in trench 15 may increase the aspect ratio evenfurther to, for example 10:1 or higher.

[0020] Once the substrate is properly positioned, a high density plasmais formed from a deposition gas to deposit a first layer of silica glasson the substrate using a deposition process that has simultaneousdeposition and sputtering components (FIG. 1, step 12). The depositiongas includes a silicon source, such as monosilane (SiH₄), an oxygensource, such as molecular oxygen (O₂), and optionally an inert gas, suchas helium (He) or argon (Ar). Referring to FIG. 2B, deposition of thisfirst layer 28 results in a partial filling of gap 15. The profile oflayer 28 within and outside of the gap will depend on the parametersused during deposition step 12 as well as the length of time of step 12.

[0021] Generally, conventional silica glass HDP-CVD depositiontechniques result in direct silicon oxide deposition on the horizontalsurfaces of the substrate, such as surface 21 within gap 15 and surfaces23 above the raised portions of substrate 20 that define the gap. Thedeposition process also results in indirect deposition (often referredto as re-deposition) of silicon oxide on sidewalls 25 due to therecombination of material sputtered from the silicon oxide film as itgrows. In certain small-width, high-aspect-ratio applications where thetechniques of the present invention are most beneficial, the continuedgrowth of the silicon oxide film results in formations 29 on the uppersection gap sidewall that grow toward each other at a rate of growthexceeding the rate at which the film grows laterally on lower portionsof the sidewall as shown in FIG. 2B. If deposition step 12 continueslong enough, the final result of this process is a void that formswithin the gap when the two opposing portions of formations 29 on theupper sidewall contact each other.

[0022] In some embodiments of the invention, the deposition of layer 28is stopped prior to or just after formations 29 contact each other and amulti-step etching process is performed that reduces the height of thelayer 28 over the raised features and widens the entry 30 to gap 15. Themulti-step etch process includes a first primarily anisotropic, physicaletch step (step 14) and a subsequent chemical etch step that isprimarily an isotropic etch (step 16). As shown in FIGS. 2C and 2D,which illustrate substrate 20 after having undergone physical etch step14 and chemical etch step 16, respectively, the etching process widensthe entry to gap 15 thereby enabling a subsequent deposition step (FIG.1, step 18) to deposit a second layer of material 34 over the substrateto completely fill the gap in a void-free manner as shown in FIG. 2E.

[0023] In some embodiments layer 34 is deposited using substantially thesame process as layer 28 in step 12. In other embodiments, however,deposition parameters for layer 34 are adjusted to optimize thedeposition-to-etch ratio (dep/etch ratio) for the aspect ratio of theremaining portion of gap 15 to be filled. In some embodiments thedep/etch ratio is between about 10-25:1 in each steps 12 and 18. Whenthe deposition process is completed, the plasma is extinguished and thesubstrate is transferred out of the chamber.

[0024] Depending on how aggressive the gapfill requirement is for aparticular application, a sequence of deposition/etch steps may berepeated multiple times before a final deposition step. Such a sequenceof repeated etch steps may include repeating the multistep etch processof steps 14 and 16 between subsequent deposition processes or may employa single one of steps 14 and 16 or a combined etch step that includesboth physical and chemical etch components in a single step. Also,passivation step 17 may be repeated after each etch sequence and beforethe next deposition sequence if desired.

[0025] In one embodiment the transition to the etching step 14 iseffected by stopping the flow of the silicon source gas, adjusting othergas flows as discussed further below and increasing the RF bias powerapplied to the substrate while maintaining the plasma from thedeposition step. Similarly, transitions to other steps also maintain aplasma in the chamber while varying gas flows, chamber pressure, RFpower levels and other parameters. Embodiments that maintain a plasmawhile transitioning to subsequent steps are performed in an in situ in asingle chamber. In other embodiments, however, the plasma isextinguished between each step, gas flows and other parameters areadjusted in preparation for the next step and a plasma is reformed. Suchembodiments can be in situ processes performed in a single chamber or indifferent chambers of a multi-chamber mainframe system or ex situprocesses performed in different chambers. In some embodiments, in situprocesses are preferred for throughput and performance reasons.

[0026] Referring to FIG. 2C, the sputtering component of etch step 14etches corners of the structure, such as film peaks 31 and formations29, at a faster rate than flat surfaces are etched. Thus, etch step 14reduces the height of layer 28 over the raised surfaces withoutsignificantly etching the bottom of the partially filled trench 15.Thus, comparing the height of these figures in FIG. 2B to those in FIG.2C, x₁-x₂ is greater than x₃-x₄. In some embodiments, x₁-x₂ is at leasttwo and a half times x₃-x₄. In other embodiments x₁-x₂ is at least fivetimes x₃-x₄ and in still other embodiments x₁-x2 is at least ten timesx₃-x₄. For example, in some embodiments x₁-x₂=1000-1500 Å whilex₃-x₄=0-400 Å. Also, in some embodiments etching at the corners occursat a rate between 3-6 times faster than etching on the flat surfaces instep 14. Etch step 14 also opens the entry to gap 30 a little bit. Etchstep 16 then uses primarily isotropic etching techniques to open theentry to gap 30 further.

[0027] The sputter etching of step 14 can be achieved by acceleratingions towards the substrate during the etching process as is known tothose of skill in the art. In some embodiments, sputtering is performedby biasing the substrate and introducing one or more sputtering agentssuch as argon, helium and/or oxygen. Other embodiments use other knownsputtering agents such as neon, xenon or similar gases. A combination ofoxygen and argon or another inert gas is used in one particularembodiment. In this embodiment, the addition of oxygen provides anadditional sputtering component and also helps improve center-to-edgeuniformity of the process. It is desirable to strictly control thesputtering process of etch step 14 so that corners 33 of the underlyingfeatures are not clipped off.

[0028] In some embodiments physical etch step 14 employs a very lowpressure of, for example, between 1.0 and 4.0 mTorr, in order to reducecollisions between ions and increase their means free path therebyincreasing the anisotropic nature of the etch process. Also, while thepredominant etching mechanism in step 14 is vertical, anisotropicsputter etching, a relatively small isotropic component may beincorporated into step 14 to prevent sputter material from redepositingon sidewall 25 thus narrowing the trench profile. To achieve thiseffect, some embodiments add a flow of between about 10-100 seem ofnitrogen trifluoride (NF₃) or a similar etchant.

[0029] In contrast to step 14, etch step 16 is primarily an isotropicetch step that etches layer 28 equally, or almost equally, in alldirections. To this end, etch step 16 employs a significantly higherflow of a reactive etchant than the reactive etchant flow used in step14. In some embodiments, the reactive etchant flow in step 16 is atleast 300 percent higher than in step 14 while in other embodiments itis at least 500 percent higher. In some specific embodiments, thereactive etchant, for example NF₃, is flowed into the chamber at a rateof between 300-600 seem NF₃. The invention is not limited to thisparticular etchant, however, and contemplates using any etchant known toetch silica glass in either step 14 or step 16.

[0030] In some embodiments, a flow of oxygen is also added to step 16 inorder to dilute the etchant gas and provide a more controllable etchrate. The relatively high volume of gas flowed into the chamber duringetch step 16 results in a considerably higher pressure than the pressureemployed in step 14. In some embodiments, chamber pressure is betweenabout 25-100 mTorr in step 16.

[0031] The combination of separate etch steps 14 and 16 allows gapshaving a particularly aggressive gapfill requirements to be completelyfilled in situations where a single etch step does not. For example, theinventors have found that in some situations a single, primarilyphysical etch step cannot widen the entry to gap 30 sufficiently for thegap to be filled in a subsequent deposition step without forming a void.Similarly, while a single, primarily chemical or purely etch step opensthe entry to gap 30 relatively quickly, it also etches the bottom of thetrench at essentially or approximately the same rate as other surfaces.Thus, in a pure chemical etch x₁-x₂=x₃-x₄ and in a primarily chemicaletch x₁-x₂≈x₃-x₄. Also, the inventors have found that the multistep etchapproach of the present invention to be superior to a single etch stepthat combines both physical and chemical etch components becauseincluding a sufficiently high flow rate of reactive etchant gas in sucha single step process to adequately open gap 30, results in the bottomof the partially filled trench being etched too quickly because of thedirectionality imparted into the process due to the bias power componentassociated with a physical etch.

[0032] In embodiments where deposition step 12 is stopped shortly afterformations 29 of film 28 contact each other forming a void within gap15, etch steps 14 and 16 reopen the gap to expose the temporarily formedvoid while widening the entry to the gap. In embodiments wheredeposition step 12 is stopped prior to formations 29 forming a void,etch steps 14 and 16 widen the gap entry.

[0033] In some embodiments, the surface of the etched film is passivated(FIG. 1, step 17) prior to depositing a second portion of the gapfillmaterial in order to remove fluorine or other halogen atoms that may beincorporated in the film due to the etching steps. In one embodiment thesurface of the film is passivated by exposing the substrate to apassivation gas that is selected to chemically react with surface of thefilm to remove any fluorine or other halogen atoms. Suitable passivatinggases include molecular oxygen (O₂), ozone (O₃), nitrous oxide (N₂O) andmolecular nitrogen (N₂) in combination with any of the preceding.Further details of techniques that can be used to passivate layer 28after an etchant step are discussed in U.S. application Ser. No.10/138,189, filed May 3, 2002, entitled “HDP-CVD DEP/ETCH/DEP PROCESSFOR IMPROVED DEPOSITION INTO HIGH ASPECT RATIO FEATURES,” and havingDongqing Li, et al. listed as coinventors which is hereby incorporatedby reference in its entirety.

[0034] Embodiments of the present invention can be implemented using avariety of high density plasma CVD substrate processing chambersincluding chambers in which a plasma is formed by the application of RFenergy to a coil that at least partially surrounds a portion of thechamber and chambers that use ECR plasma formation techniques. Anexample of an inductively-coupled HDP-CVD chamber in which embodimentsof the method of the present invention can be practiced is set forthbelow.

[0035]FIG. 3A illustrates one embodiment of a high density plasmachemical vapor deposition (HDP-CVD) system 110 in which a gapfilldielectric layer according to the present invention can be deposited.System 110 includes a chamber 113, a substrate support 118, a gasdelivery system 133, a remote plasma cleaning system 150, a vacuumsystem 170, a source plasma system 180A, a bias plasma system 180B.

[0036] The upper portion of chamber 113 includes a dome 114, which ismade of a ceramic dielectric material, such as aluminum oxide oraluminum nitride. Dome 114 defines an upper boundary of a plasmaprocessing region 116. Plasma processing region 116 is bounded on thebottom by the upper surface of a substrate 117 and a substrate support118, which is also made from an aluminum oxide or aluminum ceramicmaterial.

[0037] A heater plate 123 and a cold plate 124 surmount, and arethermally coupled to, dome 114. Heater plate 123 and cold plate 124allow control of the dome temperature to within about ±10° C. over arange of about 100° C. to 200° C. Generally, exposure to the plasmaheats a substrate positioned on substrate support 118. Substrate support118 includes inner and outer passages (not shown) that can deliver aheat transfer gas (sometimes referred to as a backside cooling gas) tothe backside of the substrate.

[0038] The lower portion of chamber 113 includes a body member 122,which joins the chamber to the vacuum system. A base portion 121 ofsubstrate support 118 is mounted on, and forms a continuous innersurface with, body member 122. Substrates are transferred into and outof chamber 113 by a robot blade (not shown) through an insertion/removalopening (not shown) in the side of chamber 113. Lift pins (not shown)are raised and then lowered under the control of a motor (also notshown) to move the substrate from the robot blade at an upper loadingposition 157 to a lower processing position 156 in which the substrateis placed on a substrate receiving portion 119 of substrate support 118.Substrate receiving portion 119 includes an electrostatic chuck 120 thatcan be used to secure the substrate to substrate support 118 duringsubstrate processing.

[0039] Vacuum system 170 includes throttle body 125, which housestwin-blade throttle valve 126 and is attached to gate valve 127 andturbo-molecular pump 128. Gate valve 127 can isolate pump 128 fromthrottle body 125, and can also control chamber pressure by restrictingthe exhaust flow capacity when throttle valve 126 is fully open. Thearrangement of the throttle valve, gate valve, and turbo-molecular pumpallow accurate and stable control of chamber pressures as low as about 1mTorr.

[0040] Source plasma system 180A is coupled to a top coil 129 and sidecoil 130, mounted on dome 114. A symmetrical ground shield (not shown)reduces electrical coupling between the coils. Top coil 129 is poweredby top source RF (SRF) generator 131A, whereas side coil 130 is poweredby side SRF generator 131B, allowing independent power levels andfrequencies of operation for each coil. In a specific embodiment, thetop source RF generator 131A provides up to 2,500 watts of RF power atnominally 2 MHz and the side source RF generator 131B provides up to5,000 watts of RF power at nominally 2 MHz. The operating frequencies ofthe top and side RF generators may be offset from the nominal operatingfrequency (e.g. to 1.7-1.9 MHz and 1.9-2.1 MHz, respectively) to improveplasma-generation efficiency.

[0041] A bias plasma system 180B includes a bias RF (BRF) generator 131Cand a bias matching network 132C. The bias plasma system 180Bcapacitively couples substrate portion 117 to body member 122, which actas complimentary electrodes. The bias plasma system 180B serves toenhance the transport of plasma species (e.g., ions) created by thesource plasma system 180A to the surface of the substrate. In a specificembodiment, bias RF generator provides up to 5,000 watts of RF power at13.56 MHz.

[0042] RF generators 131A and 131B include digitally controlledsynthesizers and operate over a frequency range between about 1.8 toabout 2.1 MHz. Each generator includes an RF control circuit (not shown)that measures reflected power from the chamber and coil back to thegenerator and adjusts the frequency of operation to obtain the lowestreflected power, as understood by a person of ordinary skill in the art.Matching networks 132A and 132B match the output impedance of generators131A and 131B with their respective coils 129 and 130. The RF controlcircuit may tune both matching networks by changing the value ofcapacitors within the matching networks to match the generator to theload as the load changes. The RF control circuit may tune a matchingnetwork when the power reflected from the load back to the generatorexceeds a certain limit. One way to provide a constant match, andeffectively disable the RF control circuit from tuning the matchingnetwork, is to set the reflected power limit above any expected value ofreflected power. This may help stabilize a plasma under some conditionsby holding the matching network constant at its most recent condition.

[0043] A gas delivery system 133 provides gases from several sources134(a) . . . 134(n) via gas delivery lines 138 (only some of which areshown). In the particular example illustrated below, gas sources 134(a). . . 134(n) include separate sources for SiH₄, O₂, Ar and NF₃ as wellas one or more sources for the extended cleaning process. As would beunderstood by a person of skill in the art, the actual sources used forsources 134(a) . . . 134(n) and the actual connection of delivery lines138 to chamber 113 varies depending on the deposition and cleaningprocesses executed within chamber 113. Gas flow from each source 134(a). . . 134(n) is controlled by one or more mass flow controllers (notshown) as is known to those of skill in the art.

[0044] Gases are introduced into chamber 113 through a gas ring 137and/or a top nozzle 145. FIG. 3B is a simplified, partialcross-sectional view of chamber 113 showing additional details of gasring 137. In some embodiments, one or more gas sources provide gas toring plenum 136 in gas ring 137 via gas delivery lines 138 (only some ofwhich are shown). Gas ring 137 has a plurality of gas nozzles 139 (onlyone of which is shown for purposes of illustration) that provides auniform flow of gas over the substrate. Nozzle length and nozzle anglemay be changed to allow tailoring of the uniformity profile and gasutilization efficiency for a particular process within an individualchamber. In one specific embodiment, gas ring 137 has 124 gas nozzles139 made from an aluminum oxide ceramic.

[0045] Gas ring 137 also has a plurality of gas nozzles 140 (only one ofwhich is shown), which in a specific embodiment are co-planar with andshorter than source gas nozzles 139, and in one embodiment receive gasfrom body plenum 141. Gas nozzles 139 and 140 are not fluidly coupled insome embodiments where it is desirable to not mix gases (e.g., SiH₄ andO₂) introduced through gas ring 137 before injecting the gases intochamber 113. In other embodiments, gases may be mixed prior to injectingthe gases into chamber 113 by providing apertures (not shown) betweenbody plenum 141 and gas ring plenum 136. Additional valves, such as 143B(other valves not shown), may shut off gas from the flow controllers tothe chamber.

[0046] In embodiments where flammable, toxic, or corrosive gases areused, it may be desirable to eliminate gas remaining in the gas deliverylines after a deposition or cleaning process. This may be accomplishedusing a 3-way valve, such as valve 143B, to isolate chamber 113 from adelivery line 138 and to vent delivery line 138 to vacuum foreline 144,for example. As shown in FIG. 3A, other similar valves, such as 143A and143C, may be incorporated on other gas delivery lines. Such 3-way valvesmay be placed as close to chamber 113 and remote plasma source 150 aspractical, to minimize the volume of the unvented gas delivery line(between the 3-way valve and the chamber). Additionally, two-way(on-off) valves (not shown) may be placed between a mass flow controller(“MFC”) and the chamber or between a gas source and an MFC.

[0047] Referring again to FIG. 3A, chamber 113 also has top nozzle 145and top vent 146. Top nozzle 145 and top vent 146 allow independentcontrol of top and side flows of the gases, which improves filmuniformity and allows fine adjustment of the film's deposition anddoping parameters. Top vent 146 is an annular opening around top nozzle145. In one embodiment, one source, e.g., SiH₄, supplies source gasnozzles 139 and top nozzle 145 through separate MFCs (not shown).Similarly, separate MFCs may be used to control the flow of oxygen toboth top vent 146 and gas nozzles 140 from a single source of oxygen.The gases supplied to top nozzle 145 and top vent 146 may be keptseparate prior to flowing the gases into chamber 113, or the gases maybe mixed in top plenum 148 before they flow into chamber 113. In otherembodiments, separate sources of the same gas may be used to supplyvarious portions of the chamber.

[0048] A remote plasma cleaning system 150, such as a microwave plasmasource or torodial plasma source, is provided to periodically cleandeposition residues from chamber components in a dry cleaning operation.The cleaning system includes a remote plasma generator 151 that createsa plasma from one or more cleaning gas source in sources 134(a) . . .134(n) (e.g., molecular fluorine, nitrogen trifluoride, otherfluorocarbons or equivalents alone or in combination with another gassuch as Argon) in reactor cavity 153. The reactive species resultingfrom this plasma are conveyed to chamber 113 through cleaning gas feedport 154 via applicator tube 155. The materials used to contain thecleaning plasma (e.g., cavity 153 and applicator tube 155) must beresistant to attack by the plasma. The distance between reactor cavity153 and feed port 154 should be kept as short as practical, since theconcentration of desirable plasma species may decline with distance fromreactor cavity 153. Generating the cleaning plasma in a remote cavitydoes not subject chamber components to the temperature, radiation, orbombardment of the glow discharge that may be present in a plasma formedin situ. Consequently, relatively sensitive components, such aselectrostatic chuck 120, do not need to be covered with a dummy wafer orotherwise protected, as may be required with an in situ plasma cleaningprocess.

[0049] System controller 160 controls the operation of system 110.Controller 160 may include, for example, a memory 162, such as a harddisk drive and/or a floppy disk drive and a card rack coupled to aprocessor 161. The card rack may contain a single-board computer (SBC),analog and digital input/output boards, interface boards and steppermotor controller boards. System controller 160 operates under thecontrol of a computer program stored on the hard disk drive or throughother computer programs, such as programs stored on a removable disk.The computer program dictates, for example, the timing, mixture ofgases, RF power levels and other parameters of a particular process.

[0050]FIG. 4 is a flowchart depicting the steps associated withdeposition of a silica glass film according to one specific embodimentof the present invention implemented in the exemplary chamber describedwith respect to FIGS. 3A-3B. The process depicted in FIG. 4 begins bytransferring a substrate into substrate processing chamber 113 (step40). Next, argon is flowed into the chamber with the throttle valve 126in a closed position in order to pressurize the chamber in preparationfor striking a plasma (step 42). Once the pressure has reached asufficient level, a plasma is formed by applying RF power to top coil129 (step 44), the throttle valve is partially opened and RF power isapplied to side coil 130 (step 46).

[0051] A flow of oxygen gas is then added to the argon flow and thethrottle valve is fully opened so that chamber pressure is set entirelyby the rate at which gases are introduced into the chamber (step 48).Next, the plasma is maintained with flows of oxygen and argon in orderto heat the substrate prior to initiating deposition of the silica glasslayer (step 50). In some embodiments, heating step 50 heats thesubstrate to a temperature of at least 400° C. and, in some otherembodiments, above 500° C. Typically heating step 50 uses source RFpower only (no bias RF power) in order to ensure the underlyingsubstrate features are not sputtered. Also, in some embodiments thesubstrate is not chucked to substrate support 113 during heating step50.

[0052] Once the substrate reaches a sufficient temperature, thesubstrate is chucked to substrate support 118 and a flow of silane isadded to the oxygen and argon flows to initiate the silica glassdeposition process (step 52). The argon flow is then stopped, the flowrates of the silane and oxygen are increased to levels optimized forgapfill capabilities during the deposition of the first portion 28 ofthe silica glass film and bias power is applied to the pedestal (step54). Some embodiments of the invention exclude a flow of argon from thedeposition gas during step 52 in order to minimize sidewall redepositionthat results in closing of the gap as discussed above with respect toFIG. 2B. Other embodiments of the invention add a flow of hydrogenand/or helium to the process gas in order to further improve gapfillcapabilities as described in U.S. patent application Ser. No.09/854,406, filed May 11, 2001, entitled “Hydrogen Assisted UndopedSilicon Oxide Deposition Process For HDP-CVD,” having Zhengquan Tan etal. listed as coinventors; and U.S. patent application Ser. No.10/137,132, filed Apr. 30, 2002, entitled “Method for High Aspect RatioHDP CVD Gapfill,” having Zhong Qiang Hua et al. listed as coinventors(Attorney Docket No. A6549/T45900) and are incorporated herein byreference in their entirety.

[0053] Deposition of first portion 28 of the silica glass layer isstopped after a predetermined time by stopping the flow of the silanesource and switching the bias power OFF (step 56). Oxygen flow isincreased slightly in step 56 in order to compensate for the stoppage ofthe silane source and prevent the plasma from being extinguished. Insome embodiments the substrate temperature reaches levels above 550° C.during the deposition of the silica glass layer. Accordingly, someembodiments maintain an unbiased, oxygen only plasma during step 56 forbetween 5-20 seconds in order to allow the temperature of the substrateto cool to a temperature less than 550° C. and preferably between 350and 500° C. Allowing the substrate to cool between deposition and etchsteps enables layer 28 to be etched in a more controllable fashion.

[0054] Next, the RF bias power is switched back ON and flows of argonand NF₃ are introduced along with the oxygen to initiate the firstphysical etch step of the multistep etch process according to theinvention (step 58). As explained above, a relatively small flow of NF₃is added to the process in order to prevent material sputtered away byoxygen and argon ions from redepositing on the sidewalls of the trench.Also, the addition of oxygen to the process improves etch uniformity aswell as providing additional sputtering.

[0055] After the completion of physical etch step 58, the flow of argonis stopped, bias power is turned OFF and the flow of NF₃ is increased aspart of a chemical etch step (step 60). Chamber pressure is alsoincreased during the chemical etch step to enable a higher etch rate.While the inclusion of oxygen along with the reactive etchant gas instep 60 is optional, it provides a number of advantages includingreducing the etch rate of the process to a more controllable rate,reducing the number of particles generated during the etch process andsubsequent deposition process and also improving the uniformity of theetch process so that fewer silicon-rich pockets (etch defects) areformed on the surface of the etched substrate. Some embodiments of theinvention introduce a hydrogen source, such as H₂, into the etchant gasin step 60 in order to improve the etch selectivity of the process tosilicon nitride and/or silicon.

[0056] As described above with respect to FIG. 1 and FIGS. 2B through2D, etch steps 58 and 60 widen the entry 30 to gap 15 while reducing theheight of material deposited over the surfaces surrounding the gapthereby enabling the gap to be filled in one or more subsequentdeposition steps.

[0057] The embodiment shown in FIG. 4 transitions from etch step 60 to asubsequent deposition step by increasing the RF power levels applied totop and side coils 129 and 130, respectively, and reducing the flowrates of NF₃ and oxygen. Then, the flow of NF₃ is stopped altogether andRF bias power is applied to bombard the surface of the substrate with anoxygen-only plasma (step 62) to reduce the amount of fluorineincorporated into the gapfill layer at the interface of the layersformed before and after the etch step as well as to reduce the number ofsilicon-rich pockets formed.

[0058] After the passivation step is completed, RF power levels for thetop and side coils as well are increased, the bias power level isincreased, the flow rate of oxygen is reduced and silane and argon areintroduced into the chamber to deposit top portion 34 of the silicaglass layer over the substrate (step 64). After top portion 34 isdeposited, the flows of silane and argon are stopped, the chamber ispurged, the plasma is extinguished and the substrate is dechucked (step66) prior to transferring the substrate out of the chamber altogether(step 68).

[0059] Depending on the height of gap to be filled as well as the widthof the gap and its profile (e.g., whether or not it has a reentrantprofile), additional etch and deposition sequences similar to the step58, 60 and 64 sequence may be repeated one or more times as necessaryprior to depositing the top portion 34 of the silica glass layer.

[0060] Table 1 below lists the process parameters according to anembodiment of the present invention implemented in the Ultima HDP-CVDchamber manufactured for Applied Materials and outfitted for 200 mmsubstrates. The gas flow rates and other parameters set forth in Table 1below are optimized for a deposition process run in the Ultima chamber.A person of ordinary skill in the art will recognize that these ratesand parameters are in part chamber specific and will vary if chambers ofother design and/or volume are employed. TABLE 1 EXEMPLARY RANGES FORPROCESS PARAMETERS Dep 1 Physical Etch Chemical Etch Dep 2 Parameter(Step 54) (Step 58) (Step 60) (Step 64) Top RF Power 3000-5100 W500-5000 W 500-2000 W 3000-5100 W (1.8 MHz) Side RF Power 3000-4800 W1500-5000 W  500-2000 W 3000-4800 W (2.1 MHz) Bias RF Power  600-4000 W100-3000 W 0 W  600-4000 W (13.56 MHz) SiH₄ Flow 20-160 sccm — — 20-160sccm O₂ Flow (1.4-2.2) ×  0-400 sccm 100-400 sccm (1.4-2.2) × SiH₄ FlowSiH₄ flow Ar Flow  0-160 sccm 50-160 sccm  0-20 sccm  0-160 sccm NF₃Flow — 10-150 sccm 300-600 sccm — Pressure 1.5-6.0 mTorr 1.0-4.0 mTorr25-100 mTorr 1.5-6.0 mTorr

[0061] Having fully described several embodiments of the presentinvention, many other equivalents or alternative embodiments of thepresent invention will be apparent to those skilled in the art. Forexample, while the invention described with respect to an undopedsilicate glass layer, the invention can also be used to improve thegapfill capabilities of phosphosilicate glass (PSG), boron-dopedsilicate glass (BSG), boron phosphosilicate glass (BPGS) layers andfluorine-doped silicon glass (FSG) as well as other types of materialsby adding an appropriate dopant gas such as PH₃ for PSG, B₂H₆ for BSG orSiF₄ for FSG in one or more of the film deposition steps. Also, in otherembodiments, an oxygen source such as N₂ 0 or CO₂ can be used instead ofO₂ and a silicon source other than monosilane may be used. Examples ofsuitable silicon sources include other silane family members such as,Si₂H₆, Si₃H₈, etc.; TEOS or SiF₄ among others.

[0062] In still other embodiments, chemical etch step 16 can beperformed by introducing remotely dissociated etchant atoms into thechamber. For example, in one embodiment, a fluorine etchant gas can beflowed into remote plasma system 150 and remotely dissociated fluorineatoms formed within system 150 can be transported to the HDP-CVD chamberto perform etch step 16. Also, while some embodiments of the inventionswitch bias power off during step 16, other embodiments may contemplateapplying a relatively small amount of bias power (e.g., 25 percent orless of the bias power applied in step 14) to the substrate during thechemical etch step. As such, the above description is illustrative andnot restrictive. These equivalents and/or alternatives are intended tobe included within the scope of the present invention.

What is claimed is:
 1. A method of depositing a film on a substratedisposed in a substrate processing chamber, the method comprising:depositing a first portion of the film over the substrate by forming ahigh density plasma from a first gaseous mixture flown into the processchamber; thereafter, sputter etching part of the deposited first portionof the film by forming a plasma from a sputtering agent introduced intothe processing chamber and biasing the plasma towards the substrate;thereafter, chemically etching part of the deposited first portion ofthe film by forming a plasma from a reactive etchant gas introduced intothe processing chamber; and thereafter, depositing a second portion ofthe film over the first portion by forming a high density plasma from asecond gaseous mixture flown into the process chamber.
 2. The method ofclaim 1 wherein the bias power is switched OFF during the chemicaletching step.
 3. The method of claim 1 wherein the first and secondgaseous mixtures are silica glass deposition gases.
 4. The method ofclaim 3 wherein the first and second gaseous mixtures each comprisesilane and oxygen.
 5. The method of claim 1 wherein the sputter etchingstep includes a flow of a reactive etchant gas that is less than a flowof the reactive etchant gas in the chemical etch step.
 6. The method ofclaim 5 wherein the reactive etchant flowed into the chamber in thesputter etch and chemical etch steps is the same gas and wherein theflow rate of the reactive etchant is at least 300 percent higher in thechemical etch step than in the physical etch step.
 7. The method ofclaim 6 wherein the flow rate of the reactive etchant is at least 500percent higher in the chemical etch step than in the physical etch step.8. The method of claim 6 wherein the reactive etchant is afluorine-containing gas.
 9. The method of claim 6 wherein the physicaletch and chemical etch steps each include a flow of an oxygen-containinggas.
 10. A method of depositing a silica glass film on a substratedisposed in a substrate processing chamber, the substrate having atrench formed between adjacent raised surfaces, the method comprising,in order: depositing a first portion of the silica glass film over thesubstrate and within the trench by forming a high density plasma processthat has simultaneous deposition and sputtering components from a firstdeposition gas comprising a silicon source and an oxygen source;stopping deposition of the silica glass film and sputter etching thefirst portion of the film by biasing a high density plasma formed from asputtering agent introduced into the processing chamber towards thesubstrate; thereafter, chemically etching the first portion of the filmwith reactive species formed from an etchant gas; and thereafter,depositing a second portion of the silica glass film over the substrateand within the trench by forming a high density plasma process that hassimultaneous deposition and sputtering components from a seconddeposition gas comprising a silicon source and an oxygen source.
 11. Themethod of claim 10 wherein the high density plasma is continuouslymaintained between the first depositing step and the sputter etchingstep.
 12. The method of claim 11 wherein the reactive species in thestep of chemically etching the first portion of the film are dissociatedremotely from a fluorine etchant gas and transported into the chamber.13. The method of claim 11 wherein the reactive species in the step ofchemically etching the first portion of the film are generated withinthe chamber by a high density plasma.
 14. The method of claim 14 whereinthe high density plasma is continuously maintained between the firstdepositing step and the second depositing step.
 15. The method of claim14 wherein the reactive etchant flowed into the chamber in the sputteretch and chemical etch steps is the same gas and wherein the flow rateof the reactive etchant is at least 300 percent higher in the chemicaletch step than in the physical etch step.
 16. The method of claim 15wherein the sputter etch and chemical etch steps each include a flow ofan oxygen-containing gas.
 17. The method of claim 16 further comprising,after the step of chemically etching the first portion of the film,exposing the first portion of the film to a passivation gas consistingof an oxygen source with or without an inert gas.
 18. The method ofclaim 16 wherein the trench is part of a shallow trench isolationstructure formed on a silicon substrate.
 19. The method of claim 16wherein the silicon source in the first and second deposition gasescomprises monosilane (SiH₄).
 20. The method of claim 19 wherein theoxygen source in the first and second deposition gases comprisesmolecular oxygen (O₂).
 21. The method of claim 20 wherein the first andsecond deposition gases each further comprise an inert gas as asputtering component.
 22. The method of claim 16 wherein the plasma isnot biased towards the substrate during the step of chemically etchingthe first portion of the film.
 23. The method of claim 10 wherein thesputter etching step etches at least two and a half times more of thesilica glass film over the raised surfaces than at a bottom of thetrench.
 24. The method of claim 10 wherein the sputter etching stepetches at least five times more of the silica glass film over the raisedsurfaces than at a bottom of the trench.
 25. The method of claim 10wherein the sputter etching step etches at least ten times more of thesilica glass film over the raised surfaces than at a bottom of thetrench.
 26. A method of depositing a silica glass film on a substratedisposed in a substrate processing chamber, the substrate having atrench formed between adjacent raised surfaces, the method comprising:forming a high density plasma within the substrate processing chamber toheat the substrate to a temperature of at least 400° C. prior todepositing the silica glass film on the substrate; maintaining the highdensity plasma while (i) flowing a first process gas comprising asilicon source and an oxygen source into the processing chamber todeposit a first portion of the silica glass film over the substrate andin the trench using a deposition process that has simultaneousdeposition and sputtering components, (ii) flowing a sputtering gascomprising an inert gas, an oxygen source and a fluorine etchant intothe process chamber while biasing the plasma towards the substrate tosputter etch the first portion of the silica glass film; (iii) switchingoff bias power that biases the plasma towards the substrate and flowinga fluorine etchant and oxygen source into the chamber in order tochemically etch the first portion of the silica glass film, wherein aflow rate of the fluorine etchant is at least 300 percent higher than aflow rate of the fluorine etchant in the sputter etch step; and (iv)flowing a second process gas comprising a silicon source and an oxygensource into the processing chamber to deposit a second portion of thesilica glass film over the first portion using a deposition process thathas simultaneous deposition and sputtering components.
 27. The method ofclaim 26 wherein the sputter etch and chemical etch steps each include aflow of an oxygen-containing gas.
 28. The method of claim 27 wherein thetrench is part of a shallow trench isolation structure formed on asilicon substrate.
 29. The method of claim 26 wherein the sputteretching step etches at least two and a half times more of the silicaglass film over the raised surfaces than at a bottom of the trench. 30.The method of claim 26 wherein the sputter etching step etches at leastfive times more of the silica glass film over the raised surfaces thanat a bottom of the trench.
 31. The method of claim 26 wherein thesputter etching step etches at least ten times more of the silica glassfilm over the raised surfaces than at a bottom of the trench.